BACKGROUND: Increased lactate is an important biochemical marker in diagnosis of children with suspicion of mitochondrial disorders. A diagnostic dilemma may originate if analyses are performed after seizures, when the increased lactate levels may be considered to result from the seizures. To address this problem, we ascertained the diagnostic value of lactate and alanine in blood (B) and cerebrospinal fluid (CSF) in children with mitochondrial disorders (n = 24), epilepsy (n = 32), psychomotor retardation (n = 23), meningitis (n = 12) and meningism (n = 16). METHODS: Lactate concentration was measured using a spectrophotometric method. Amino acids in serum and CSF were analyzed by ion exchange chromatography with ninhydrin detection. RESULTS: Average blood and CSF-lactate levels were significantly higher in children with mitochondrial disorders (3.87 ± 0.48 and 4.43 ± 0.55 mmol/l) and meningitis (2.77 ± 0.45 and 8.58 ± 1.08 mmol/l) than in children with epilepsy (1.72 ± 0.13 and 1.62 ± 0.04 mmol/l), psychomotor retardation (1.79 ± 1.40 and 1.68 ± 0.06 mmol/l) or meningism (1.70 ± 0.13 and 1.64 ± 0.07 mmol/l). Blood and CSF-alanine levels were also higher in children with mitochondrial disorders (558 ± 44 and 51 ± 8 μmol/l) than in children with epilepsy (327 ± 23 and 27 ± 3 μmol/l) or psychomotor retardation (323 ± 27 and 26 ± 3 μmol/l). The CSF-lactate levels of children with epilepsy were similar whether the samples were obtained 3 ± 0.6 h after an attack of brief seizures or from children without history of recent seizures. CONCLUSION: Elevated cerebrospinal fluid lactate level is a reliable marker pointing to mitochondrial origin of disease, even in children who have recently suffered short-lasting seizures. Some children with mitochondrial disorders manifest only mild or intermittent elevation of lactate levels.

Department of Pediatrics and Adolescent Medicine 1st Faculty of Medicine Charles University Prague Czech Republic

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Neonatal onset of mitochondrial disorders in 129 patients: clinical and laboratory characteristics and a new approach to diagnosis